A. Field of the Invention
The present invention relates to programmed manipulator apparatus and more particularly to an arrangement whereby the programmed manipulator base may remain fixed and the manipulator arm moved through a series of programmed steps in coordination with a continuously moving workpiece. The programmed recorded data is calculated from statically-taught positions with the conveyor stopped wherein a series of steps over a portion of the workpiece are taught. While the invention is particularly suitable for and will be described in connection with the welding of car bodies, or the like, it will be understood that the arrangement of the present invention is equally suitable for performing other types of operations on a continuously moving workpiece.
B. Description of the Prior Art
Programmed manipulators of the type shown, for example in Dunne, et al. U.S. Pat. No. 3,661,051, have been employed in the past to perform various types of operations on conveyor carried workpieces. Thus, in Devol U.S. Pat. No. 3,283,918 an arrangement is shown wherein the programmed manipulator is bodily moved on rails parallel to a continuously moving conveyor and in timed relation with the workpiece so that there is no relative movement between the programmed manipulator and the workpiece during the working cycle. While this arrangement is generally suitable for its intended purpose, it has the disadvantage that the bodily movable programmed manipulator requires a considerable amount of floor space which must be considered off limits for human operators and hence a large amount of space is required to perform the required welding operations on a given car body, or the like. In addition, the entire programmed manipulator must be moved along the rails and because of the weight of the manipulator, the services that must be provided such as welding cables, air hoses, and the like, and the length of movement of the manipulator along these rails, the equipment necessary to move the manipulator along these rails is the most expensive of any of the motions of the programmed manipulator. Furthermore, installation of a rail system to carry one or more programmed manipulators along a given conveyor line is costly and disruptive of production during installation, servicing and the like.
Another arrangement which has been heretofore used in connection with the welding of car bodies on an automobile assembly line is to employ a so-called indexing or start-stop conveyor line in which the car bodies are sequentially moved to different stations opposite a group of fixedly positioned programmed manipulators and the conveyor is held stationary while a given welding operation is performed on a given car body at each station. Such an arrangement has the disadvantage that the indexing conveyor moves considerably slower than a continuously moving conveyor since the car bodies must be stopped at each station during the entire welding operation performed by a programmed manipulator. In addition, the complexity of the conveyor drive system necessary to stop the conveyor accurately at each programmed manipulator station considerably increases the cost of the overall conveyor system required. Furthermore, and most importantly, when an indexing conveyor system is employed, it is not practical to mix human operators in with programmed manipulators on a given conveyor line because the human operators will always have to be protected with safety buttons and then the entire conveyor line will move only as fast as the slowest operator on the line.
Engelberger, et al. U.S. Pat. No. 3,744,032 discloses another conveyor arrangement whereby the stationary based manipulator may be programmed by successively stopping the workpiece at different closely spaced locations along the conveyor path, successively moving the manipulator arm to positions corresponding to the different points on a representative workpiece when the workpiece is positioned at the different locations, and recording the corresponding position to which the arm is successively moved. While this arrangement is also generally suitable for its intended purpose, it has the disadvantage that the conveyor must be moved precisely a small amount such as 1/2 to 1 inch every time a point is recorded. Movement of the entire conveyor line by such a small increment is almost impossible to accomplish with any degree of accuracy. Accordingly, the particular car body to be programmed or reprogrammed is usually unhitched from the main conveyor line and either programmed at a separate location or at the same location while the main conveyor line remains down. Such a recording procedure is costly and time consuming despite the fact that the procedure only approximates the effects of conveyor movement.